Skid-Mounted Equipment (Static/Rotary) Foundation

Start by asking the question "what is it supposed to do".

When you have that answer then decide what you need to make it do that.

When you have those items then mount it to the skid.

No, really your gonna have to do some of the work here, that's what they hired your for.

What makes you think it needs a foundation. Skid mounted equipment is done for the ease of movement or replacement for number of reasons. It may not be in one place long enough to warrent a foundation. Good packed crush and run may do. These are question you need to find the answers to. We can't see the island from here and we are not the end user. So how are we to answer the question.

A flat floor with some softwood plank offcuts to plonk the skid on might be all it needs, Boss, but I can't see what you're doing.

I can testify that for equipment requiring precise alignment, such as a 300hp, end driven turbine compressor, rigidity or the ability to re-align after transport/bedding in, are key factors.

Is there a rule of thump for calculating size,composition etc of concrete foundation for

a)stationary items,b)rotating mass whose weight,inertia etc are known,c)IC engine etc

I am retired and without my notes, books etc. But off hand I can say provide a square or rectangular RCC pad. If your equipment is viberating to and fro, you need the foundation to weigh 3 to 4 times the weight of your equipment.